How To calculate Resistors Connected In Series And Parallel

Resistors can be connected in series or in parallel. Each type of connection has different way of calculating its total equivalent resistance.

In this article you will learn:

  • How to calculate the total equivalent resistance of resistors connected in series.
  • The effect of resistors  in series.
  • How to calculate the total equivalent resistance of resistors connected in parallel.
  • The effect of resistors in parallel.

 

Resistors In Series

Resistors are said to be connected in “ Series “, if it is connected end-to-end within a circuit or together in a single line. Resistors in series have the same amount of current passing through them but have different voltage in them. We can calculate the voltage in each resistor by using voltage divider theorem. The amount of current is the same for a set of resistors connected in series.

For resistors connected together in series, the total resistance or the total equivalent resistance of the circuit must be equal to the sum of all the individual resistors added together i.e by taking the individual resistive values. The equivalent resistance of a circuit is the single value of resistance that can replace any number of resistors in series without changing the values of the voltage or the current in the circuit.

Note: The equivalent or total resistance has the same effect on the circuit as the original combination of resistors.

Resistors In Series

Series Resistor Equation

If two resistors in series have the same resistive value,let say 1KΩ (1000 ohms) , then the equivalent resistance will be 1KΩ + 1KΩ = 2KΩ. If three resistors in series are unequal and of different values, then the total or equivalent resistance, R is equal to the mathematical sum of the three resistances. That is equal to R + R + R. If four or more unequal (or equal) resistors are connected in series then the equivalent resistance is: R + R + R + R +….. etc. One essential point to note about resistors in series is that the total equivalent resistance of two or more will always be greater than the value of the largest resistor in the network.

Example

Resistors In Series

The equivalent resistance of the resistors in the diagram will be 500 + 900 + 600 = 2000 (2KΩ)

 

Resistors In Parallel

Resistors are said to be connected in parallel if there are multiple paths for the flow of current in the parallel network. Resistors connected in parallel have the same voltage across them but have different amount of current flowing through them. Resistors in parallel are connected to the same two points (nodes) to a common voltage source. In order to calculate the current flowing in each resistor connected in parallel, current divider theorem is used.

Resistors in parallel

 

Parallel Resistor Equation

For resistors in parallel the equivalent resistance R is calculated differently unlike the ones connected in series. Here, the reciprocal ( 1/R ) value of the individual resistances value are all added together. The inverse of the equivalent resistance of two or more resistors connected in parallel is the algebraic sum of the inverses of the individual resistances. If the two resistances in parallel are equal (the same value, let say 1KΩ and 1KΩ) Then the equivalent resistance, R is equal to half (500Ω) the value of one of the resistors. That is 1/R =1/1000 + 1/1000 = 500

For three equal resistors in parallel, it is one-third (R/3) the value of one of the resistors,etc. It is important to note that the equivalent resistance is always less than the smallest resistor in the parallel network of resistors. Therefore, the total resistance, R will always decrease as more parallel resistors are added.

 

Example

resistors in parallel

The equivalent resistance of the resistors above will be 1/R = 1/3 + 1/2 + 1/5 = 0.968 (968mΩ), mΩ means milliohms.

Magneto Resistor

 

A magneto resistor is a resistor of which its electrical resistance varies or changes as a result of presence of external magnetic field. A magnetic field is a region in space where the effect of magnetic force is felt by a body/object placed near it. Magneto resistors have a variable resistance which is subject to the magnetic field intensity. A Magneto resistor can be utilized to gauge magnetic field intensity, presence and direction. They are otherwise called magnetic dependent resistors (MDR). A magneto resistor is a subfamily of magnetic field sensors or magnetometers.

Magneto resistor sysmbol
Magneto resistor symbol (European)
magneto-resistor
Magneto resistor symbol (American)

 

 

 

 

 

How A Magneto Resistor Works

The magneto resistor will experience change in resistance when placed in a magnetic field. The resistance of the magneto resistor increases/decreases when the strength of the magnetic field is increased/decreased I.e it is proportional to the strength of the magnetic field. This change occurs as a result of magneto resistive effect. In the absence of magnetic field, the charge carriers (electric current) in the material move in a straight path until magnetic field is applied to the material, the magnetic forces cause the mobile charge carriers to change their direction from direct path to indirect path. This increases the length of electric current path. As result of this, large amount of free electrons collides with the atoms and loses their energy in the form of heat and only a small amount of free electrons flow through the conductive path. The small amount of free electrons moving from one place to another place carries the electric current. Therefore, the resistance of the material increases with increasing magnetic field.

 

Magneto Resistive Effect

Magneto resistive effect is the property of some materials, which makes them to change their resistance under the presence of magnetic field. This effect was first discovered by an Irish mathematician, physicist and engineer called William Thomson, otherwise known as Lord Kelvin in 1856. This effect is noticed in semiconductors, non-magnetic metals, and magnetic metals (like ferromagnetic) materials and it is dependent on the magnetic field intensity and the angle between the direction of electrical current and the magnetic field. This effect is therefore known as (AMR). 

Permalloy, an alloy comprising 81% nickel (Ni) and 19% iron (Fe) has a high anisotropic magneto resistance as well as a low magnetostriction (change in size due to magnetic fields) which makes it a preferred material for magneto resistors.

Magneto resistors are usually made of long thin films of permalloy. In order to increase the sensitivity of a permalloy magneto resistor, shorting bars of aluminium or gold are placed on the thin permallow films at an angle of 45 degrees. This forces the current to flow in a direction of 45 degrees proportional to the length of the film. This is called a barber pole configuration. A typical AMR magnetoresistive sensor is made of a combination of 4 permalloy thin film magnetoresistors, connected in a wheatstone measurement bridge. Most routine magneto resistors use the AMR impact.

 

Types Of Magneto Resistive Effect

Magneto resistive effects are of 4 types:

  • Giant Magneto Resistance (GMR)
  • Extraordinary Magneto Resistance (EMR)
  • Tunnel Magneto Resistance (TMR)
  • Collosal Magneto Resistance (CMR)

 

Giant Magneto Resistance (GMR)

Giant Magneto Resistance was discovered by Albert Fert and Peter Grunberg in 1988. This effect is observed in the ferromagnetic materials. The resistance of the ferromagnetic material is dependent on the whether the magnetization of adjacent ferromagnetic layers are aligned parallel or anti-parallel. The resistance is large for the ferromagnetic layers with anti-parallel alignment whereas the resistance is small for the ferromagnetic layers with parallel alignment.

 

Extraordinary Magneto Resistance (EMR)

The extraordinary magneto resistive effect was discovered in the year 2000. The magnetic field effect of Extraordinary Magneto Resistance (EMR) is much greater than Giant Magneto Resistance (GMR). The EMR effect occurs in semiconductor metal hybrid systems when a transverse magnetic field is applied. In the absence of magnetic field, the resistance of the semiconductor metal hybrid system is very small whereas in the presence of strong magnetic field, the resistance of semiconductor metal hybrid system is large.

 

Tunnel Magneto Resistance (TMR)

In 1975 M. Julliere discovered the Tunnel Magneto Resistance (TMR). The Tunnel Magneto Resistance (TMR) occurs in Magnetic Tunnel Junction (MTJ). Magnetic Tunnel Junction (MTJ) is a component comprises two ferromagnets separated by an insulator. The electrons will flow from one ferromagnet to another ferromagnet through the tunnel barrier or insulator. The amount of electric current (charge carriers) moving through the tunnel is dependent on the orientation of magnetizations.

If the magnetic field is applied to Magnetic Tunnel Junction in such a way that the direction of magnetizations of ferromagnet is aligned in a parallel manner, a large amount of electrons flow easily. As a result, electric current increases and resistance decreases. Likewise, if the magnetic field is applied in such as way that the direction of magnetizations of ferromagnet is aligned in an anti-parallel manner, only a small number of charges carriers (free electrons) flows through the tunnel and large amount of free electrons are blocked. As a result, electric current decreases and resistance increases.

 

Collosal Magneto Resistance

Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides , which enables them to dramatically change their electrical resistance in the presence of a magnetic field . It was first discovered by G.H. Jonker and J.H. Van Santen in 1950s. The magnetoresistance of conventional materials enables changes in resistance of up to 5%, but materials featuring CMR may demonstrate resistance changes by orders of magnitude. More info here.

 

Applications of magneto resistors

The various applications of magneto resistors include:

  • Angle position sensors
  • Bio-sensors
  • Position sensors
  • Linear position sensors
  • Rotary position sensors
  • Hard disk drives
  • Ferrous metal detection
  • Magnetic field sensors
  • Vehicle and traffic detection
  • Electronic compass
  • Magneto resistors are used in electronic compass formeasuring earth’s magnetic field.
  • Magneto resistors are used for measuring electric current.
  • Magnetometry,measurement of magnetic field intensity and direction

Reference: Resistor Guide, Physics and Radio Electronic

VARISTOR:A Type of Resistor

VARISTOR

A varistor is a type of resistor in which its resistance is dependent on the voltage applied. The word is composed of parts of the words “VARiable resISTOR” i.e their resistance varies. The resistance of the varistor decreases when the voltage increases. They are made of semiconductors elements. It can also be called voltage dependent resistor (VDR). The most common type of VDR is the metal oxide varistor (MOV). it has a nonlinear, non-ohmic current–voltage characteristic which is similar to that of a diode .

Varistor , voltage dependent resistor

 

 

 

 

 

 

Types Of Varistors

The most important types of varistors are:

  • Metal oxide varistor (MOV)– It is a nonlinear transient suppressor composed of a ceramic mass of zinc oxide (ZnO) oxide grains, in a matrix of other metal oxides (like small amounts of bismuth, cobalt, manganese) sandwiched between two metal plates (the electrodes).
  • Silicon carbide varistor – This type of varistor were commonly used before the MOV come into the market. This component uses silicon carbide (SiC). They have been intensively used in high voltage, high voltage applications. One of the disadvantages of this component is that it draws a significant standby current.

 

Varistor comes in different shapes/packages they are:

  • Disc shaped varistor- It is circular in shape.
  • Axial leaded varistor- It is spherical.
  • Radial leaded varistor-  It has a square shape.
  • Block shaped varistor- It is the largest of the aforementioned and rectangular. It is used for higher power rating.

Applications And Uses Of Varistors

  • They are used as surge protector devices or power strips.
  • They are used to protect communication lines. Varistor used for this purpose have low capacitance.
  • They are also used for wide variety of applications which include:
  • Low voltage board level protection
  • Power supply protection
  • Radio communication equipment transient suppression
  • Cable TV system surge protectors
  • Microprocessor protection
  • Transient voltage surge suppressor (TVSS)
  • Car electronics protection
  • Industrial high energy AC protection
  • Electronics equipment protection

 

Thermistor

What Is A Thermistor

A thermistor is a special type of resistor whose resistance is dependent on temperature I.e its resistance varies or changes in response to temperature. The resistance of a thermistor decreases with increasing temperature. This is due to the properties of the semiconductor material that the thermistor is made with. It derived it name from the term “thermally sensitive resistor”. They are made up of ceramics and metal oxides. Thermistor was first discovered by Michael Faraday in 1833.

NTC thermistor

Thermistor is divided into two types they include:

1. Negative Temperature Coefficient (NTC) Thermistor– This type of thermistor, resistance decreases with temperature to protect inrush over voltage conditions and it is installed in parallel in a circuit.

2 .Positive Temperature Coefficient (PTC)– This type of thermistor, the resistance increases with temperature to protect against over current conditions and it is installed in series in a circuit.

 

Uses And Applications Of Thermistors

  • They are used for voltage regulation, volume control, time delays, and circuit protection.
  • They are used in circuit (surge) protector to prevent over current from damaging an electrical or electronic device plugged in.
  • They are used in digital thermometers to accurately measure someone’s temperature. They are inexpensive, reliable and respond quickly,that is why they are used in digital thermometers.
  • They are used in Microwave to determine and regulate the internal temperature (prevent overheating which could lead to fire)
  • They are used in recharging of rechargeable batteries to prevent the charger from getting too hot.
  • They can be used in the making of fire alarm.
  • They are used in automotive (cars, trucks and buses) to determine the temperature of oil and coolants. Unlike its usage in microwave, they do not prevent or regulate the vehicle from overheating rather it serves as a signal to know when the car is overheated. They connected to indicators on the dashboard of the automotive.
  • Thermistors are can also be used to regulate temperatures for safe and cost effective operations in the handling and processing of food item.💨💨

 

Reference: Facstaff , Omega , Sensorsci

 

 

 

Photo Resistor-Light Dependent Resistor

Some resistors are dependent on physical quantities like light, heat, magnetic force, etc. These resistors can be divided into 4 types which includes:

• Photo resistor (LDR)

• Thermistors (NTC and PTC)

• Varistor (VDR)

• Magneto resistor (MDR)

 

Photo Resistor

Photo resistor is an electronic component whose resistivity depends on the presence or absence of light.Photo resistor is also known as Light Dependent Resistor (LDR), photo conductors, photo conductive cells or photocells cells. Hence, they are light sensitive components. They are made from light sensitive material like camdium sulfide. Photo resistor has no fixed value of resistance, it’s resistivity varies with light level available. Thus,it acts like a variable resistor. When the light level decreases, the resistance of the photo resistor increases and when the light level increases, the resistance of the photo resistor decreases. Therefore the resistance of a photo resistor is maximum in the dark.

LDR, photo resistor

Working Principle of Photo Resistor

A photo resistor works on the principle of photo conductivity. Photo conductivity is an optical phenomenon in which the materials conductivity is increased in the presence of light. In the presence of light, photo resistor absorbs the light rays (photons). Then the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. This process is known as exication. Therefore when light having adequate energy hits on the device, more and more electrons are excited to the conduction band which results in huge number of charge carriers . The result of this process is more and more current starts flowing through the device when the circuit is closed and hence it is said that the resistance of the device has been decreased.

 

Types Of Photo Resistor

Intrinsic Photo Resistor– This type of LDR is made of undoped materials like germanium or silicon. Light rays (photons) that fall on the device excite electrons from the valence band to the conduction band, and the result of this process are more free electrons in the material, which can carry current, and therefore less resistance. 

Extrinsic Photo Resistor– This type of LDR is made of materials doped with impurities, also known as dopants. The dopants create a new energy band above the existing valence band, populated by electrons. These electrons need less energy to make the transition to the conduction band thanks to the smaller energy gap. The result is a device sensitive to different wavelengths of light.

 

Applications Of Photo Resistor

 They are usually used as light sensors or in making automatic night light.

 They are usually used in a camera light meter where there is a need to detect absences or presences of light.

 They used in burglar alarm circuits and light intensity meters.

 

Reference:Resistor guide , Electrical4u

Difference Between Series And Parallel Connections

In any electronic or electrical system there are two ways to make connections which predict how current will flow in a circuit. They are series and parallel connections.

Series circuit
Series Connection

Series Connection

This is the connection where there is only one possible path through which current can flow in a circuit. It is also the end-to-end connection of components (loads) within a circuit. When loads are connected in series, the loads will have the same amount of current flowing through them not considering what the loads (components) are used in the circuit or what their values are but will have different voltage across the loads. Series connections have a common switch. One of the disadvantages of series connection is that if one load or component fails, then all the components in the circuit fail too. However, this can also be an advantage of series connection if it was made to protect a device. For Example a fuse is usually connected in series to the components of the device to be protected. When a fuse gets burnt for instance as a result of high current, then the device it protects will not be damaged because current will no longer get to it.

parallel Circuit
ParallelConnection

Parallel Connection

A parallel connection is the connection in which there are several paths through which current flows in a circuit. In a parallel connection, the loads will have the same voltage but different current flowing in it. Most parallel connections usually have different switches for each load.

Note: If a circuit has only one switch for its loads, it doesn’t automatically make it a series connection. Some parallel connections can also be controlled by one switch. Unlike series connection, the failure of one load in a circuit does not lead to the failure of other loads in a parallel connection. In electrical wiring parallel connection requires more wires when compared to series connection.

 

Applications Of Series And Parallel Connection

The use and application of series and parallel circuit connection cannot be over emphasized in both electrical and especially electronic connections. The application of series and parallel connection can be clearly seen in our homes, school halls, in our street lights, electronic devices like TV, radio and so on.

Parallel connection makes it possible for us to connect loads to their individual switch with the push of a button, street lights is an example of parallel connection. Some cell phone won’t power on without the battery even if the charger is being connected to it, this is an example of series connection. However, if it does power on without the battery when its charger is connected to it, then it’s a parallel connection.

The application of series and parallel connections are used in numerous electronic and electrical devices.

 

Trimmers:A Type Of Variable Resistor

TRIMMERS

A Trimmer is a small (miniature) like potentiometer which is used for adjustment, tuning and calibration or recalibration in electronic/electrical circuits. It can be also be called preset resistor when it is wired as a rheostat or trimpots. Preset resistor are usually mounted on printed circuit boards and it is adjusted by using screwdriver. It is designed for infrequent adjustment as the lifespan is often only 200 cycles.The most commonly used resistive element in trimmer is either carbon composition or cermet.

Trimmers ,Trimpots

Types Of Trimmers

There are different types of trimmers available in the market which have different mounting methods(through smd and hole), adjusting orientations (top or side) as well as single and multi-turn variations.

Single Turn Trimmer

Single turn trimmers are very common and are usually used where a resolution of one turn is enough. They are one of the cheapest variable resistors available.

Multi Turn Trimmer

Multi turn trimmer are used for higher adjustment resolutions. it takes several turns of the adjustment screw to reach the end value. The numbers of turns varies between 5-25, but the most common are 5, 12 or 25 turns. They are made by using a worm-gear (rotary track) or leadscrew (linear track) mechanism to achieve the high resolution. They are more expensive than single turn trimmers due to their more complex construction and manufacturing.The lead screw packages can have a higher power rating due to their increased surface area.

Rheostats: A Type Of Variable Resistors

RHEOSTAT

A rheostat is a type of variable resistor that is used to control electric current flowing in a circuit. The word rheostat was coined by an English scientist called Sir Charles Wheatstone. it is derived from the Greek word “rheos” and “statis” which means a stream controlling device or a current controlling device. They are used to vary the resistance in a circuit without interruption. Just like potentiometer, rheostat have 3 terminals for connections. It uses only two out of the three terminals for connections. The first connection is made to one end of the resistive element and the other to the wiper. Rheostat is made up of a resistive element (wire is wound around an insulating ceramic core) and a wiper (sliding contact) slides over the windings.

Rheostat Symbol
Rheostat Symbol

Types Of Rheostats

There are many types of rheostats. The rotary type is the most used in power control applications like the control speed of a motor. Just like potentiometers, multi-gang types are also available. They are used to regulate multiple applications in parallel or to increase the power rating without interruption of power. Freely rheostats can be fitted with a mechanical stop to limit the minimum or maximum resistance.

Slide rheostats are also available and usually used for education and in laboratory environments. Both Linear and slide rheostats are made of resistive wire wound on an insulating cylinder. A sliding contact is often used to increase or decrease the resistance, thereby increases or decreases the current flowing in the circuit.

Applications Of Rheostat

Rheostats were usually used as power control devices, for example,used as a dimmer i.e  to control light intensity, speed of motors, heaters and ovens. Rheostats are often used for tuning and calibration in circuits. Motor controllers also use rheostats to control a motor’s  velocity by limiting the flow of current. Rheostats are also used in many small devices likeblenders, mixers, fans, and power tools. Furthermore,it can be used as a test device to give a reference resistance value(s).

Potentiometer:A Type Of Variable Resistor

A Variable resistor is a resistor that does not have fixed value of electrical resistance, that is the value of electrical resistance can be varied or adjusted..

Variable resistor can be divided into 3 types, they are:

  1. Potentiometer
  2. Rheostat
  3. Trimpot

Potentiometer

A potentiometer is a 3 terminals variable resistor which has a rotating or a sliding contact. The first and third of the 3 terminals are connected to both ends of a resistive material while the second terminal is connected to a sliding contact which is called a wiper. The wiper moves over the resistive material. The location of the wiper decides the output voltage of the potentiometer. If only two terminals are used, one end and the wiper, then it acts as a rheostat. The potentiometer imperatively acts as a variable voltage divider. The common name of a potentiometer is  potmeter or pot .The  materials  used to construct potentiometers, include metal film, carbon composition, wirewound or cermet.

 

Types Of Potentiometers

There are many varieties of potentiometers. They can be categorized into 2 types:

  1. Manually adjustable potentiometer (rotary or linear).
  2. Digital potentiometer

1)Manually adjustable potentiometer- Manually adjustable potentiometer can be divided into two broad types, which includes:

  • Rotary potentiometers
  • Linear potentiometers

Rotary Potentiometers

This is the most common type of potentiometer where the wiper turns along a round path. They are mostly and commonly used in audio system for increasing or decreasing of volume. A rotary potentiometer is divided into 5 types namely:

  • Single-turn potentiometer
  • Multi-turn potentiometer
  • Dual-gang potentiometer
  • Concentric potentiometer
  • Servo potentiometer
Rotary potentiometer
Single Turn Potentiometer
Rotary potentiometer
Dual gang potentiometer

 

 

 

 

 

 

Rotary potentiometer
Concentric potentiometer
Linear Potentiometers

This is a type of  Potentiometer where the wiper (slider or fader) moves along a linear path. There are 4 types of linear potentiometers, they are

  • Single slide potentiometer
  • Dual-slide potentiometer
  • Multi-slide potentiometer
  • Motorized slider potentiometer
Linear potentiometer
Single Slide Potentiometer
Linear potentiometer
Dual Slide Potentiometer
Linear potentiometer
Motorized Slide Potentiometer
Digital Potentiometers
Type of resistor
Digital Potentiometer

Digital potentiometers are potentiometers which are controlled  or by digital signals I and switches instead of by mechanical action. Another name for digital potentiometer is digipot or digital resistor. A digital potentiometer is built from a resistor ladder ( a string of small resistors in series)  integrated circuit. A digipot can be used control up/down signals or protocols such as  I²C and Serial Peripheral Interface (SPI).

 

Standard Values of Potentiometers

Most potentiometers have common values such as 1K, 2K,5K,10K, 100K ohm,etc.The most used value for potentiometers is 10K ohm.

General Applications Of Potentiometers

The applications of potentiometers are numerous, it will be difficult to mention all of it here.Below are few applications of it:

  • They are used for measurement of distances or angles ( single slide pot).
  • They are used in joysticks for machine control.
  • They are used in audio system for volume control and balance.
  • They are used in calibration and tuning of circuits performance.

 

Materials Used For Potentiometer

  • Carbon composition
  • Wirewound
  • Conductive plastic
  • Cermet

Fixed Resistor And Its Types

There are vast types of resistors, they can be classified into 3 which are:

• Fixed resistor

• Variable resistor

• Resistor dependent on physical quantity

Fixed Resistor

A Fixed resistor is a resistor that has fixed value of electrical resistance which is not adjustable. Fixed resistor is divided into 7 sub types which include:

Fixed Resistor
Carbon Composition Resistor

i. Carbon composition Resistor (CCR)–  It is made out of fine carbon particles (graphite) mixed with ceramic dust (clay) and resin. The mixture is pressed into sticks under high pressure and temperature, thereafter has a solid form. Carbon composition resistors are usually used for the protection of circuits against surge, high voltage power supplies, high energy pulses and welding.

Carbon Film Resistor
Carbon Film Resistor

ii. Carbon Film Resistor (CFR)– It is made out of a ceramic carrier with a thin pure carbon film around it, that acts as a resistive material. This process occurs at high temperature and under high pressure. Carbon film resistor is used in high voltage and temperature devices.

Metal Film Resistoe
Metal Film Resistor

iii. Metal Film Resistor (MFR)– It is made of a thin metal film (resistive element) deposited on a ceramic body. They are generally used for high frequency or radio frequency applications due to its low noise and temperature stability characteristics.

Metal Oxide Film Resistor
Metal Oxide Film Resistor

iv. Metal Oxide Film Resistor- It is produced with chemical deposition processes which involves the reaction of a pure metal with a gas at low pressure and at a high temperature. Metal Oxide film resistor has better high surge current capability with a much greater temperature rating than metal film resistors.

Wirewound Resistor
Wirewound Resistor

v.Wirewound Resistor- Wirewound Resistor  is made by winding an insulated metallic wire around a core of non-conductive material (ceramic, glass or plastic). The insulated metallic wire usually used has high resistivity. An alloy like Nickel-chromium (Nichrome) or a copper-nickel-manganese alloy called Manganin are used as the residtive element.

Other alloys that can be used as insulated metallic wire include:

• Silver alloys

• Nickel Chromium alloys

• Copper alloys

• Iron Chromium alloys

• Iron Chromium Aluminum alloys

There are three types of wirewound resistor they are:

• Precision wirewound

• Power wirewound

• Potentiometer wirewound

Wirewound resistor can be used as fuse or in circuit breaker.

vi. Metal Foil Resistor- The metal foil resistor is made of an alloy of usually Nichrome with some additives. It is placed on a ceramic carrier which has high heat conductivity. Metal foil resistor is usually used in circuits where noise caused within the circuit (like audio systems) is to be averted. They also used in electronic scales because of its low noise, low temperature coeffient resistance (TCR) and a low thermal electromotive force value.

vii. Surface mount Device (SMD)– SMD resistor is  made of a ceramic substrate and onto this is deposited a metal oxide film. SMD resistor is small and rectangular in shape. It is mostly used in electronic devices like cell phones, mp3 and so on due to its size.